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The dynamic ramming technique

For the dynamic pipe installation with the ramming method, pneumatically driven pipe ramming machines are applied. Open steel pipes as casing or product pipes of up to 4000 mm in diameter, in lengths of up to 80 m and in soil grades 1 - 5 (in certain cases even in soil grade 6 - readily soluble rock) can be installed very economically without the need for jacking abutments beneath railway tracks, motorways and rivers.

 

 

 

The pneumatically driven rammer is cylindrically shaped, with a front or rear taper for connecting the interchangeable cone, cotter segments and/or soil removal cones or adapters which provide a tight-fitting connection between the machine and the pipe. If soil removal cones or adapters are used, some of the soil core which is carried back along the pipe and can escape through two rear positioned gaps, thus providing internal spoil tension release. The onset of impact segments prevents flaring of the pipes and enables butt-welding of the single pipe lengths. The welding beads of spiral welded pipes have to be smoothed level with the pipe material within the area of the segment fixing depth in order to prevent point compression loads.

The machine is powered by a conventional job-site compressor. After professional welding, the single pipe lengths are rammed forward successively, due to a robust one-piece construction, impact energy of 40,000 kN can be achieved by with the largest TRACTO-TECHNIK rammer at full capacity; this is optimally passed along the complete pipe string right up to the pipe cutter. An average installation speed of 10 m/h can be achieved.

After ramming, the soil is completely removed either by water pressure alone or with a combination of air pressure. Applying the suitable safety measures, soil removal up to ND 500 is also allowed with air pressure alone with larger pipe diameters calling for manual soil removal using other auxiliary devices (Please refer to the operating manual!).

According to the latest investigations by Prof.  Dr. Stein, the wall thickness calculation following ATV-A 161 and GW 312 is possible; examinations, however, have proved that the strain of the external soil pressure, due to the weight of the soil and the dynamic traffic loads, is clearly smaller in dynamically driven steel pipes than the corresponding comparative value gained for pipes installed by a trenchless method according to ATV-A 161. It should be possible to reduce the wall thickness of the pipes using this method.

The machines have proven successful in practice - the Ruhrgas AG rate them as “recommended”. Judging from a constructional point of view, the Bahn AG prefers cased methods like the ramming system to uncased methods. The ramming method is described in the German guideline ATV-A 125 and in the GW 304 Pipe Laying as well as in other German standards.

Advantages of the method:
 

  • Minor disruption to valuable ground surfaces (road surfaces, gardens etc.), therefore little restoration required - high economical advantage
  • Low social costs by avoiding diversions, road cones, barriers, setting up traffic lights and signalling systems etc.
  • Recognised method
  • Short set-up times - short pipe installation times
  • The dynamic impact method can breakthrough obstacles and overcome increased ground resistance with less effort, when restarting after welded joint down times
  • The target precision is improved because the dynamic impact method breaks alternating soil formations within the pipe diameter range; obstacles need not be displaced in one piece or pushed forward
  • No jacking abutment and no conveyor spiral auger which may get jammed
  • The soil core remains inside the pipe during installation, thus no penetration of water when undercrossing rivers or high water level ground conditions
  • Only minimal pipe cover is required, i.e. no elaborate pits
  • Simple technology
  • Adaptable to all pipe diameters with interchangeable ram cones
  • Wide range of applications possible 


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